A well-known imam and a worshipper were killed in a bombing of a popular mosque in Kabul's fortified Green Zone on Tuesday, officials said.
The latest attack in the Afghan capital came after seven civilians were killed in the north of the country in a roadside bomb blast that authorities blamed on the Taliban.
No group immediately claimed responsibility for the evening explosion at one of Kabul's most famous places of worship.
The blast sent shockwaves through the sprawling militarised zone, where alarms sounded at embassies and international offices, sending staff rushing into safe rooms.
"Unfortunately, this evening some explosives placed by terrorists in Wazir Akbar Khan mosque detonated," Afghan Interior Ministry spokesman Tareq Arian said.
The mosque is at the main entrance to the Green Zone and is accessible from inside and outside the tightly controlled area.
Top leaders often go there to pray.
The mosque's imam, Ayaz Niazi, was one of those killed, Mr Arian said.
Mr Niazi was famous in Kabul and his sermons were often so well attended that worshippers would spill into the grounds outside the mosque.
Mr Arian initially said the attack was conducted by a suicide bomber but the cause later became less clear.
President Ashraf Ghani's spokesman called the incident a heinous attack.
On Saturday, ISIS bombed a television station's minibus in central Kabul, killing a journalist and the driver.
Seven civilians were killed late on Monday by a roadside bomb linked to the Taliban in northern Afghanistan, despite authorities pressing for peace talks with the militants and a ceasefire over the Eid Al Fitr holidays.
The blast struck a small lorry in Kunduz province carrying a group of labourers in the volatile Khan Abad district.
No group claimed responsibility, but Kunduz provincial spokesman Esmatullah Muradi blamed the Taliban.
"The Taliban usually plant roadside bombs to target security forces, but their bombs usually kill civilians," Mr Muradi said.
Two of the six wounded in Kunduz were in critical condition, district chief Hayatullah Amiri said.
Violence across much of Afghanistan has dropped since May 24, when the Taliban announced the surprise three-day ceasefire for Eid.
Mr Ghani welcomed the truce offer and authorities announced about 2,000 Taliban prisoners would be released in a "goodwill gesture", with a view to starting peace talks.
Afghanistan's former chief executive, Abdullah Abdullah, who has been appointed to lead the talks, has said his team was ready to begin negotiations "at any moment".
US Secretary of State Mike Pompeo held a video conference on Monday with top officials including Mr Ghani and his first deputy Amrullah Saleh.
Mr Saleh stressed the importance of the continuing drop in violence and the need to maintain a ceasefire.
The two sides discussed the future steps needed to bring peace in Afghanistan, Mr Ghani's office said.
Releasing Taliban prisoners and the venue for the intra-Afghan peace talks were discussed, it said.
Violence surged after the Taliban signed a landmark agreement with the US in February, which paved the way for the withdrawal of all foreign forces by May next year.
